If it was truly a loan, was it to the daughter directly or to her incorporated business?
If the latter as a matter of law the debtor continues to owe the principal back to the estate according to the terms of the loan. The child who is the business' principal owner (and I assume 1/5th beneficiary of the estate) would take her 1/5th share of the estate (including 1/5th of the loan). If the loan was to the daughter, the daughter presumably owes the money to the estate (unless debts were forgiven at death, or to be treated as advances on a bequest, under the Will). If the loan balance exceeded her share of the estate, she as debtor would owe money to the estate, and get nothing.
HOWEVER, this sounds like something different than a normal loan, and either an advance, or an investment in the business with the return to have been (or having become) "salary" for little or no real work. Perhaps the loan should be treated as an equity investment.
Thus this may be a time for a grieving family to try to put aside any petty family jealously and resolve this in a manner that is "fair", rather than purely "legal"; sometimes getting everything purely legal can cost huge dollars, create conflict that breaks a family apart and creates generations of resentment and conflict. As everyone has his or her view as to what may be "fair" (the daughter whose business it is could think forgiving the loan, and still giving her 1/5th of the estate, is fair -- it is not), while one child might say "that was her share, we'll split the rest in 4", and another might say "I want sister to pay the estate back every penny, plus interest, and not credit the salary, even if it sends her to bankruptcy as she shouldn't get more than me".
This is time for the family to turn, as one, to a very good lawyer-mediator and resolve it.